<!DOCTYPE html>
<html>
<head><title>Frontend</title></head>
<body>
  <h1>Hello from Frontend</h1>
  <button onclick="callApi()">Call Backend</button>
  <p id="output"></p>

  <script>
    async function callApi() {
      const res = await fetch('$BACKEND_URL');
      const data = await res.json();
      document.getElementById('output').innerText = data.message;
    }
  </script>
</body>
</html>
